Qubit Platform Single Electron on Solid Neon

The Quest for an Ideal Quantum Bit: A New Qubit Breakthrough Could Revolutionize Quantum Computing

A new qubit platform: electrons from a heated luminous filament (top) land on a solid neon (red block), where a single electron (represented by a wave function in blue) is trapped and manipulated by a superconducting quantum circuit (patterned chip at bottom). Credit: Courtesy of Dafei Jin/Argonne National Laboratory

A new qubit platform could transform quantum information science and technology.

You are no doubt reading this article about a digital device whose basic unit of information is the bit, either 0 or 1. Scientists around the world are rushing to develop a new type of computer based on the use of quantum bits, or qubits.

In an article published on May 4, 2022, in the journal Nature, a team led by the US Department of Energy’s (DOE) Argonne National Laboratory has announced the creation of a new qubit platform formed by freezing neon gas into a solid at very low temperatures, sputtering electrons from the filament of a light bulb on the solid, and trap a single electron there. This system has the potential to be developed into perfect building blocks for future quantum computers.

“It would seem that an ideal qubit is on the horizon. Thanks to the relative simplicity of the electron-on-neon platform, it should lend itself to easy fabrication at low cost. — Dafei Jin, Argonne scientist at the Center for Nanoscale Materials

To make a useful quantum computer, the quality requirements for qubits are extremely demanding. Although there are different forms of qubits today, none is optimal.

What would make an ideal qubit? It has at least three exceptional qualities, according to Dafei Jin, an Argonne scientist and principal investigator of the project.

It can stay in a simultaneous 0 and 1 state (remember the cat!) for a long time. Scientists call this long “coherence”. Ideally, this time would be around one second, a time step that we can perceive on a home clock in our daily life.

Second, the qubit can be changed from one state to another in a short time. Ideally, this time would be about one billionth of a second (nanosecond), a time step of a typical computer clock.

Third, the qubit can be easily linked to many other qubits so that they can work in parallel with each other. Scientists call this bonding an entanglement.

Although currently well-known qubits are not ideal, companies like IBM, Intel, Google, Honeywell and many startups have chosen their favorite. They actively pursue technological improvement and commercialization.

“Our ambitious goal is not to compete with these companies, but to discover and build a fundamentally new qubit system that could lead to an ideal platform,” Jin said.

Although there are many choices of qubit types, the team chose the simplest – a single electron. Heating a single luminous filament that you might find in a child’s toy can easily produce an unlimited amount of electrons.

One of the challenges for any qubit, including the electron, is that it is very sensitive to disturbances in its environment. So the team chose to trap an electron on an ultrapure solid neon surface in a vacuum.

Neon is one of the few inert elements that does not react with other elements. “Because of this inertia, solid neon can serve as the cleanest possible solid in vacuum to house and protect all qubits from disturbances,” Jin said.

A key component of the team’s qubit platform is a chip-scale microwave resonator made of a superconductor. (The much larger home microwave oven is also a microwave resonator.) Superconductors – metals with no electrical resistance – allow electrons and photons to interact together near[{” attribute=””>absolute zero with minimal loss of energy or information.

“The microwave resonator crucially provides a way to read out the state of the qubit,” said Kater Murch, physics professor at the Washington University in St. Louis and a senior co-author of the paper. “It concentrates the interaction between the qubit and microwave signal. This allows us to make measurements telling how well the qubit works.”

“With this platform, we achieved, for the first time ever, strong coupling between a single electron in a near-vacuum environment and a single microwave photon in the resonator,” said Xianjing Zhou, a postdoctoral appointee at Argonne and the first author of the paper. “This opens up the possibility to use microwave photons to control each electron qubit and link many of them in a quantum processor,” Zhou added.

“Our qubits are actually as good as ones that people have been developing for 20 years.” — David Schuster, physics professor at the University of Chicago and a senior co-author of the paper

The team tested the platform in a scientific instrument called a dilution refrigerator, which can reach temperatures as low as a mere 10 millidegrees above absolute zero. This instrument is one of many quantum capabilities in Argonne’s Center for Nanoscale Materials, a DOE Office of Science user facility.

The team performed real-time operations to an electron qubit and characterized its quantum properties. These tests demonstrated that the solid neon provides a robust environment for the electron with very low electric noise to disturb it. Most importantly, the qubit attained coherence times in the quantum state competitive with state-of-the-art qubits.

“Our qubits are actually as good as ones that people have been developing for 20 years,” said David Schuster, physics professor at the University of Chicago and a senior co-author of the paper. “This is only our first series of experiments. Our qubit platform is nowhere near optimized. We will continue improving the coherence times. And because the operation speed of this qubit platform is extremely fast, only several nanoseconds, the promise to scale it up to many entangled qubits is significant.”

There is yet one more advantage to this remarkable qubit platform.“Thanks to the relative simplicity of the electron-on-neon platform, it should lend itself to easy manufacture at low cost,” Jin said. “It would appear an ideal qubit may be on the horizon.”

Reference: “Single electrons on solid neon as a solid-state qubit platform” by Xianjing Zhou, Gerwin Koolstra, Xufeng Zhang, Ge Yang, Xu Han, Brennan Dizdar, Xinhao Li, Ralu Divan, Wei Guo, Kater W. Murch, David I. Schuster and Dafei Jin, 4 May 2022, Nature.
DOI: 10.1038/s41586-022-04539-x

The team published their findings in a Nature article titled “Single electrons on solid neon as a solid-state qubit platform.” In addition to Jin and Zhou, Argonne contributors include Xufeng Zhang, Xu Han, Xinhao Li and Ralu Divan. In addition to David Schuster, the University of Chicago contributors also include Brennan Dizdar. In addition to Kater Murch of Washington University in St. Louis, other researchers include Wei Guo of Florida State University, Gerwin Koolstra of Lawrence Berkeley National Laboratory and Ge Yang of Massachusetts Institute of Technology.

Funding for the Argonne research primarily came from the DOE Office of Basic Energy Sciences, Argonne’s Laboratory Directed Research and Development program and the Julian Schwinger Foundation for Physics Research.

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